pidfile: Use new svc_find_by_pidfile() in plugin
pidfile: Use new svc_find_by_pidfile() in plugin

A service may now have a custom PID file, possibly because it doesn't
really create one itself.  This needs to be taken into account also in
the pidfile plugin.

Signed-off-by: Joachim Nilsson <583c295fd7602c168ad814279bbc3894ba65f5d6@gmail.com>

troglobit/finit,troglobit/finit